The ultrastructural features of embryonic human and rodent palatal epithelium are being investigated in an attempt to become familiar with the details of secondary palate formation. Scanning electron, transmission electron, and light microscopy are being conducted on all stages of palatal tissues from 5 weeks to 12 weeks (post-fertilization) in the human. In addition, histochemical studies principally aimed at an examination of surface coats and glycoprotein synthesis in the palatal epithelium, are being conducted. Emphasis is placed on those stages of palate development just prior to fusion in an effort to determine the mechanism of epithelial-epithelial adherence. An in vitro system for studying human palatal development is being developed so that experimental manipulation (incorporation of labeled precursors, exposure to teratogens) may be conducted.